This invention relates to a closure for obturating a marrow cavity.
Hip joint prostheses are usually anchored in the marrow cavity of the femur by means of a bone cement composed of polymethyl methacrylate, introduced into the marrow cavity in a pasty form. Then the prosthesis shaft is pressed into the plastic mass and the cement is permitted to harden completely. Care must be taken that the bone cement is introduced into the marrow cavity to a depth which is just sufficient to allow the cement to reliably fill all of the area between the bone and the prosthesis shaft once the prosthesis shaft has been inserted. The pressure generated during the insertion of the prosthesis shaft is intended to compact the bone cement in order to maintain the formation of cavities due to the inclusion of air at a low level, and to cause the cement to better conform to the contours of the marrow cavity. This is more difficult if the still plastic cement is able to escape into the free marrow cavity during insertion of the prosthesis shaft.
To prevent an undesirable escape of bone cement, various closures for marrow cavities have been developed, namely those of endogenous materials (that is, bone spongiosa) and synthetic materials. Such a marrow cavity closure or block must be composed of body-compatible materials. Additionally, the closure should be deformable since, under certain circumstances, the closure must seal the marrow channel at a location beyond its narrowest point and usually at a location whose cross section deviates from the ideal circular shape. Moreover, it is advisable that the material not only be body-compatible but also resorbable by the body as quickly as possible since it no longer has any useful function once the cement has hardened which occurs in about 15 minutes.
Marrow cavity blocks made of bone spongiosa exhibit good body compatibility, they are quickly resorbed or transformed. A drawback of such blocks is that they are practically non-deformable and that they constitute a greater risk of infection compared to marrow cavity blocks made of synthetic materials because they can be disinfected only within limits. They also require a longer time for surgery, if they are made of bone material that is obtained during the same surgical procedure, for example, from the severed joint head.
Although the prior art marrow cavity blocks of synthetic materials, such as dextrose, are easily sterilized and are quickly resorbed by the body, due to their lack of deformability, they have only a limited sealing effect. These materials, to be sure, are able to swell, but the time available is too short to take advantage of this property.